Coffee

Moka pot is probably the hardest common brew method to get right. If everything is coming out as sour, from specialty roasters to super dark grocery store beans, it’s most likely a process/technique issue rather than the brewer. I can give a few suggestions:

1. Explore grind size more thoroughly. While marketing says it can be used for moka pot, it’s probably stretching its limits and I wouldn’t trust published chart numbers on range. Typically, if it’s sour, it’s under extracted and you should go with a finer grind size and increasing the amount appropriately. In another comment, you said going coarser gave better results so can try going even coarser as it’s possible it’s to too fine and over pressure is causing some form of channeling. Also, probably do a once over on your grinder, making sure everything is put together well and is zero’d properly.
2. Double check the recipe you are using matches your pot size. Moka Pots come in different sizes so using a recipe for a larger/smaller pot could yield poor results.
3. How are you applying heat? Constant heat until it’s done or taking it off/on based how it’s brewing? What does the stream of coffee look like, is it smooth and almost syrupy or bubbly and violent? As long as you are starting low and the stream is coming out smooth, I probably wouldn’t worry about heat much. If it’s coming out fast and bubbly though, turn down the heat or remove it from the heat completely when it starts going.
4. Make sure you aren’t over tightening the pot. While it should be hand tight, you shouldn’t need to crank it super hard. You did mention that 5-10 ml leaks out which shouldn’t happen but could if its too tight due to overpressure.

Lightly roasted coffee is often more sour than darker roasts

Mokas are a finicky beast. I’ve had it make some of the worst and some of the tastiest cups I’ve had. Is it acidic or bitter? It’s easy to burn it, but that doesn’t sound like the problem. I’m guessing it’s too fine. Every bag I got had to be individually dialed on, but in general I found a grind much more similar to drip/ pour over worked best. I’d try that. Fill your filter up to where there’s a good mound and lightly tap down with a spoon.

Also, have your changed your filter and gasket that go into the top portion? Those can get old grinds stuck in it easy that can taste off.

It may be that you're under-extracting it, a finer grind size would be the next thing to try.

Another thing to highlight is that lighter roasts have more acidity, so it may also be the beans you've got

Tamp it evenly